Methods and apparatus for drill stem testing



Dec. 9, 1969 A. z. GRIFFIN, JR 3,482,628

METHODS AND APPARATUS FOR DRILL STEM TESTING Filed Dec. 29. 1967 Arcfi/e Z. f/ff/f), Jr:

INVENTOR.

ATTORNEY United States Patent 3,482,628 METHODS AND APPARATUS FOR DRILL STEM TESTING Archie Z. Griflin, Jr., Denver, Colo., assignor to Schlumberger Technology Corporation, New York, N.Y., a

corporation of Texas Filed Dec. 29, 1967, Ser. No. 694,731 Int. Cl. E21b 47/06, 47/00, 33/16 US. Cl. 166-152 2 Claims ABSTRACT OF THE DISCLOSURE Drill stem testing apparatus and methods wherein the pressure below the packer is gradually reduced after opening the test valve to prevent the .application of shock loads to the tools and the formation, thereby enabling even dry tests at great depths in the earth under extremely high pressure conditions without damage to the tools or the formation.

This invention relates generally to formation testing, and more specifically to drill stem testing apparatus and methods for testing earth formations under high pressure differential conditions without damage to the tools or the formation.

In drill stem formation testing, a temporary completion of a formation is made by isolating the formation zone from control fluids in the well bore with a packer and then opening a tester valve to permit formation fluids to flow from the isolated formation zone into the pipe string. The tester valve can next be closed to permit pressure recorders to record a fluid pressure build-up curve as a function of time from which many significant formation parameters can be determined.

It will be appreciated that to induce connate fluids to flow from the formation into the isolated zone, the pressure in the isolated zone, which initially has the static head of the control fluids, must be reduced. This can be accomplished by running the pipe string into the well dry so as to provide a low pressure chamber which can be communicated with the isolated zone. In any event, before the tester valve is opened, the control fluids in the well bore exert a flotation force or buoyancy on the pipe string which may be of considerable magnitude in a relatively deep test. When the test valve is opened, the flotation or buoyancy force is fairly suddenly lost as fluids enter the pipe string which can result in the application of substantial shock loads to the testing tool, the packer and pressure recorders, which shock loads may cause damage to the tools. Such conditions are at the most extreme when a dry test is made, e.g., the formation fails to produce any fluids. Moreover, a sudden reduction in fluid pressure in the isolated zone can cause damage to the formation itself. Either of these occurrences is, of course, highly undesirable.

The present invention has for its primary object the provision of methods and apparatus for testing at substantial depths and under very high pressures, wherein the above-mentioned problems caused by shock loads upon opening the test valve are obviated. More specifically, the application of shock to the tools and the formation is prevented in accordance with this invention.

Summary of the invention The present invention may be summarized from a conceptual standpoint as a method and apparatus for drill stem testing comprising the procedural steps of lowering a packer and test valve into a well bore or a pipe string and setting the packer to isolate a formation zone to be tested from the well control fluids. The test valve is then opened to reduce the fluid pressure in the zone and thus 3,482,628 Patented Dec. 9, 1969 enable flow of fluids from the formation. To prevent sudden loss of flotation or buoyancy force, a liquid is displaced ahead of formation fluids entering the tools, and a gradual reduction in pressure in the well bore zone is effected by choking the flow of liquid into the pipe string. By virtue of the gradual pressure reduction, the buoyancy force is not suddenly lost but is dissipated over a period of time and in a controlled manner so that neither the tools nor the formation are damaged.

Apparatus in accordance with the present invention comprises an expansible packer coupled to a testing tool and adapted for suspension on a pipe string in the well bore. The packer is arranged to be expanded to seal off the Well bore and isolate a formation zone from the control fluid in the well bore. The testing tool includes a valve which can be opened to admit an initial flow of formation fluids into the pipe string and which can be closed to shut the formation in again in order to permit measurements of the initial formation fluid pressures. A chamber sub is located between the tester valve and a choking valve and contains a suitable clean liquid such as fresh water. The choking valve initially functions to choke the flow of liquid into the pipe string for a period of time and can be operated in response to manipulation of the pipe string to eliminate the choking effect. During the choking period, there is a gradual reduction in pressure in the isolated zone so as to prevent sudden loss of buoyancy force on the tools. Moreover, inasmuch as the liquid is forced to flow through the choke valve means ahead of the formation fluids, the choke will not become plugged before the well bore pressure adjacent the isolated zone has been fully reduced. Eventually the choke valve can be operated by the pipe string to open the same to full flow conditions. Use of the present invention enables very deep testing as above described, with the consequently great hydrostatic pressures acting on the tools and the formations, and even under the extreme pressure conditions of a dry test at great depths without damage to the tools or the formation.

The present invention has other concepts and advantages which will become more clearly apparent in connection with the following detailed description. A preferred embodiment of the apparatus in accordance with the present invention is shown in the accompanying drawings in which:

FIGURE 1 is an elevational schematic view of a string of tools in a well bore for conducting a formation test; and

FIGURE 2 is a more detailed view of the choking valve used to control the rate of pressure reduction when the test valve is opened.

Referring initially to FIGURE 1, there is depicted schematically a string of tools which may be used to test earth formations traversed by a well bore in accordance with this invention. The string of tools is suspended on a running-in string of tubing or drill pipe 10 and can include an expansible packer 11 shown and described in US. Patent No. 3,280,917 to I. W. Kisling, III, a perforated anchor 12 which carries conventional inside and outside pressure recorders 13, a bypass valve 14 and a valved tester tool 15 shown and described in US. Patent No. 3,308,887 to B. P. Nutter. The particular details of these structures are not a part of the present invention and any conventional tools for performing the same function as these tools may be used. It will be appreciated that with the anchor 12 resting on the bottom of the well bore, the weight of the string 10 can be imposed upon the tools to effect expansion of the packer 11 into sealing engagement with the borehole wall as well as closure of the bypass valve 14. Thus the formation zone to be tested is isolated from control fluids or drilling mud in the well bore above the packer 11, and the pipe string 10 provides a fluid communication path between the isolated zone and the earths surface. The valved tester can be opened and closed by manipulation of the pipe string, and the pressure recorders 13 provide a permanent record of fluid pressure values vs. time in the isolated zone, which record can be used to evaluate various formation parameters as will be apparent to those skilled in this art.

A chamber sub such as, for example, a joint of drill pipe, is coupled to the inner mandrel of testing tool 15. The chamber sub 20 is filled with a clean liquid such as plain water. Coupled to the upper end of the chamber sub 20 is a valved flow controlling tool 22 which is shown in more detail in FIGURE 2. The tool 22 includes an inner mandrel 23 adapted for rotation within an outer tubular housing 24 and connected at its upper end by a collar 25 to the pipe string 10. The lower end portion of the outer housing member 24 is threadedly connected to the upper end of the chamber sub 20. The outer housing member 24 has an upper thickened section 26 which is sealed against the inner mandrel by a suitable packing structure 27. A split ring 28 is contracted around the mandrel 23 and is conveniently removable for maintenance of the packing structure 27. A bearing assembly 29 can be located between the collar 25 and the split ring 28 to transmit loads from the mandrel to the housing and to reduce frictional resistance to rotation of the mandrel relative to the housing.

An intermediate section 31 of the housing has internal longitudinal splines 32. Below the splines 32 is an inwardly extending section 33 having a downwardly depending sleeve 34 which is laterally spaced from the inner wall of the housing member to provide an annular flow passage 35 in communication with ports 36 through the wall of the sleeve. A tubular valve member 37 is telescopically received within the bore of the sleeve 34 and has a closed lower end portion 38 and spaced upper and lower ports 39 and 40. The ports 39 and 40 are arranged for selective registry with the sleeve ports 36 in spaced longitudinal positions of the valve member 37 relative to the sleeve 34. Upper seals 52 and 53 are located above and below the upper valve ports 39 and like seals 54 and 55 are located above and below the lower valve ports 40, the respective seals engaging the inner wall surface of the sleeve. Preferably, the upper valve ports 39 are small relative to the lower ports 40 for purposes which will be more clearly described hereafter.

The valve member 37 is connected to an annular head 42 having external longitudinal splines 43 engaging the internal housing splines 32 to slidably and corotatably secure the head to the housing member. A threaded sleeve 44 extends upwardly from the head 42 and has internal right-hand jack threads 45 which mate with companion external threads 46 on a lower end portion of the inner mandrel 23. Inasmuch as the head 42 cannot rotate within the housing member 24, rotation of the inner mandrel 23 relative to the housing member will effect vertical feeding of the head and thus the valve member 37 relative the sleeve 34 with consequent selective opening and closing of the orts 39 and 40. In order to confine fluid flowing through the tool to the bore 47 of the inner mandrel 23, a wash pipe 48 can extend between the head 42 and the lower end portion of the inner mandrel 23, and suitable seals 49 and 50 prevent fluid leakage. As previously mentioned, the chamber sub 20 is initally filled with liquid 56, and the pipe string can be initially dry or empty to provide a low pressure chamber as will be familiar to those skilled in the art.

Operation In operation, the string of tools is lowered into the well until the anchor 12 rests on bottom with the packer 11 located above the formation zone to be tested. The test valve in the tester tool 15 is closed, the chamber sub 20 is filled with liquid, and the pipe string can be dry and thus provide an, atmospheric or low pressure chamber. With the tools properly positioned, the weight of the pipe string ltlis imposed thereon to elfect expansion of the packer 11, closing of the bypass valve 14 and opening of the tester valve. Opening of the tester valve initiates a reduction in pressure in the isolated zone below the packer 11 and permits fluids to flow upwardly in the tools. Upward flow of formation fluids displaces the fluid 56 from the chamber sub 20 through the ports 36 and 39 and into the pipe string 10.

By virtue of the fact that the upper valve member ports 39 are of relatively small size, there is a substantial choking effect to the flow of the liquid 56 from the chamber sub 20 into pipe string 10 ahead of the formation fluids. Accordingly, there is a gradual reduction in pressure below the packer 11. After a lapse of time, for example 3 to 4 minutes, there will have been a sufficient gradual reduction in pressure so that the choking effect of the tool 22 can be eliminated without the danger of shock to the tools or the formation. Accordingly, the pipe string 10 can be rotated to the right to feed the valve member 37 upwardly relative to the sleeve 34 until the large ports 40 come into registry with the sleeve ports 36, whereupon the formation fluids and any liquid remaining in the chamber sub 20 can flow in unimpeded fashion into the pipe string 10 where the same can be conducted toward the surface. When desired, the tester tool 15 can be closed by manipulation of the pipe string in conventional manner for the recordal of a shut-in pressure build-up curve by the recorders 13. Of course, the tester tool 15 can be recycled as many times as desired for additional recordings. When the test has been completed, the bypass 14 is opened to equalize pressures and the packer 11 unseated so that the string of tools can be withdrawn from the Well. The fluid sample in the pipe string 10 can be removed in conventional manner and the sample together with the pressure recordings can be used to evaluate the formations characteristic properties.

It will be appreciated that since the present invention eliminates possible damage to the tools due to shock loads upon sudden loss of buoyancy when the tester is opened, use of the invention permits the performance of even a dry test at substantially greater depths than has heretofore been possible in the art. It should be further noted that even though the choking ports 39 might eventually be plugged by debris in the formation fluids, a good test may still be obtained because the volume of the chamber sub 20 permits adequate fluid displacement and pressure reduction to occur before the ports could have a chance to plug. Therefore, even if the ports should plug, the testing tool can be shut-in to obtain a pressure build-up recording. Moreover, even if the small choke ports 39 plug, the larger ports 40 can be registered with the sleeve ports 36 and the test can be continued.

It will be appreciated that although the drawings illustrate the present invention in connection with a set-down packer and bottom hole anchor, a hook-wall, straddle or other packer and anchor system can be used. Since certain changes may be made in the present invention without departing from the concepts thereof, it is intended that the appended claims shall cover all such changes or modifications falling within the true spirit and scope of the present invention.

I claim:

1. Apparatus for use in dry string drill stem testing procedures at substantial depths below the earths surface comprising: packer means and valved tester means adapted for suspension in a well bore on a pipe string; choke valve means at the lower end of the pipe string; chamber means coupled between said choke valve means and said valved tester means; a substantially noncompressible, clean liquid filling said chamber means, said liquid being displaced ahead of the formation fluids when the valved tester means is opened; and port means in said choke valve means for restricting the flow of said liquid therethrough to eflect a gradual reduction in fluid pressure below said packer means and adjacent the formation, thereby preventing the application of shock loads to said tester means and packer means due to sudden loss of buoyancy force as Well as preventing damage to the formation itself due to a sudden reduction in pressure.

2. The apparatus of claim 1 wherein said choke valve means further includes flow ports of larger area than said port means; and means responsive to manipulation of the pipe string for placing said flow ports in the flow path to enable unrestricted flow of formation fluids into the pipe string.

References Cited UNITED STATES PATENTS DAVID H. BROWN, Primary Examiner US. Cl. X.R. 

